1. Field of the Invention
This invention relates to an improved process for the preparation of complex mixtures of branched chain fatty acids or esters and more particularly, to methods for substantially increasing the amounts of monomeric branched products and decreasing the amounts of polymeric products when monounsaturated fatty acids or esters are heated in the presence of certain combinations of catalysts.
2. Description of the Art
It is known in the art that dimer and polymerized fatty materials may be prepared either from unsaturated fatty acids or fatty acid esters by heating them with or without a clay catalyst. The starting fatty acids or esters employed in these polymerization reactions have been described as being either monounsaturated or polyunsaturated fatty materials. In the prior art the main objective has usually been the production of dibasic or dimerized fatty acids or esters.
In the course of preparing polymerized fatty acids it is customary to separate the dibasic or dimerized fatty acids from unpolymerized fatty acids, usually by distillation. These unpolymerized fatty acids are referred to as the monomeric fraction. In effecting the polymerization of unsaturated fatty acids or esters, a secondary reaction occurs concurrently, which results in a structural modification of a portion of the monomeric unsaturated fatty acid or ester. Such structural modification of the starting fatty material does not permit further polymerization. The structurally modified or isomerized fatty acids are formed to a greater or lesser degree as co-products of all thermal methods of polymerizing unsaturated fatty acids either in the presence or absence of a natural clay catalyst. A number of modifications of the dimerization reaction of unsaturated fatty acids and esters have been reported in the prior art, all with the intention of improving the conversion of starting fatty acids to the dibasic or dimer fatty acids. The most widely practiced modification of the process is to employ water in the polymerization process to suppress decarboxylation leading to hydrocarbon products. The most widely used catalysts, are the natural crystalline clays such as the montmorillonites.
It is also known in the art that use of 1,2-dichloroethane as a co-catalyst with an acid clay catalyst increased somewhat the yield of branched chain acids over that obtained with only the clay catalyst.
Under the most favorable conditions employed for the dimerization or polymerization of unsaturated fatty acids a portion of the starting fatty acid does not polymerize. This unpolymerized material is typically separated from the polymerized acids by distillation and is commonly referred to as the monomeric fraction. This monomeric fraction is known to contain saturated fatty acids originally present in the starting material or formed in the course of the polymerization reaction, structurally modified or branched chain fatty acids and unchanged or only slightly modified unsaturated fatty acids. The structurally modified or branched chain fatty acids are not shorter chain fatty acids produced by cracking, are in the C.sub.16 -C.sub.18 range and retain most of the original unsaturation of the starting fatty acids. The branched chain acids are usually separated from the unmodified fatty acids by hydrogenation to saturated fatty acids followed by low temperature crystallization which removes the normal chain fatty acids. In most instances the amount of branched fatty acids produced does not exceed the amount of the dimeric fatty acids formed and typically they are formed in minor amounts.